The present invention relates to an aluminum alloy brazing sheet capable of fluxless joint in an inert gas atmosphere, a brazing process using the same, and a brazed product using the same.
An aluminum brazing process has been used for manufacturing heat exchangers and panels as it is an efficient method capable of making joints with large areas and joints with multiple points. For these multi-point joints, a brazing sheet clad with a brazing material as a covering material of a core material which in turn serves as a structural material is generally used by virtue of an arrangement efficiency of the brazing material for the joints.
Three brazing methods, namely, (1) a fluxless method in vacuum, (2) a non-corrosive flux method in an inert gas atmosphere, and (3) a corrosive flux method in air, have hitherto been used.
Among these methods, there have been problems because method (1) requires an expensive vacuum furnace, method (2) requires an airtight atmosphere furnace which is cheaper than the vacuum type but relatively expensive, a flux coating process, and an expensive inert gas which is consumed, and method (3) requires a large amount of labor and cost for processing a corrosive flux before and after brazing although it is excellent in apparatus and consumable expense.
In the light of these problems, for example, a method has been proposed in which brazing without flux is carried out in a nitrogen atmosphere using a brazing sheet comprised of an Alxe2x80x94Sixe2x80x94Mgxe2x80x94Bi brazing material, as shown in Welding Journal, Oct. 1983, page 31.
However, this method has been still problematic in that an oxidation film on an original sheet must be controlled to be thin and a flow of nitrogen gas must be increased for prevention of oxidation.
It is therefore an object of the present invention to provide an aluminum alloy brazing sheet capable of fluxless joint in a simpler inert gas atmosphere, dissolving the problematic issues in the related art as described above.
According to a first aspect of the present invention, there is provided an aluminum alloy brazing sheet which comprises: a thin covering material; a core material; and an Alxe2x80x94Si alloy brazing material as an intermediate material interposed between the thin covering material and the core material, wherein the thin covering material and the core material comprise aluminum alloy shaving a solidus temperature higher than a liquidus temperature of the brazing material so that the molten brazing material seeps onto a surface of the thin covering material when the brazing material is molten in an inert gas atmosphere, thereby allowing fluxless brazing.
This arrangement enables substantial reduction in the production cost, partly because brazing can be carried out without expensive installations such as a vacuum furnace and an airtight atmosphere furnace, and flux, and partly because the least inert gas is consumed. It also renders the braze-assembling work easy because the brazing sheet can be placed in a desired position easily. In addition, the inventive arrangement leads to provision of braze-assembled products that exhibit excellent corrosion resistance.
Desirably, the Alxe2x80x94Si alloy brazing material further contains one or two of from 0.1 to 5% (by mass; the same hereinafter) of Mg and from 0.01 to 0.5% of Bi.
The Alxe2x80x94Si alloy brazing material, may further contain one, two or three of from 0.1 to 5% of Zn, from 0.01 to 0.1% of In, and from 0.01 to 0.1% of Sn.
According to a second aspect of the present invention, there is provided an aluminum alloy brazing sheet brazing process is provided which comprises the steps of: providing an aluminum alloy brazing sheet comprised of a thin covering material, a core material, and an Alxe2x80x94Si alloy brazing material as an intermediate material interposed between the thin covering material and the core material, wherein the thin covering material and the core material comprise aluminum alloys having a solidus temperature higher than a liquidus temperature of the brazing material, and conducting brazing using the brazing sheet but without flux in an inert gas atmosphere.
According to a third aspect of the present invention, there is provided a product which is braze-assembled by an aluminum alloy brazing sheet brazing process which comprises the steps of: providing an aluminum alloy brazing sheet comprised of a thin covering material, a core material, and an Alxe2x80x94Si alloy brazing material as an intermediate material interposed between the thin covering material and the core materials, wherein the thin covering material and the core material comprise aluminum alloy shaving a solidus temperature higher than a liquidus temperature of the brazing material, and conducting brazing using the brazing sheet but without flux in an inert gas atmosphere.